A Simple Formula for the Calculation of Peak Values of Currents Induced in Overhead Lines by Indirect Lightning Strokes. Theory and Experimental Validation

The electromagnetic field due to lightning strokes propagates at grazing angles, if, as it is generally assumed, the lightning channel is considered as a straight vertical antenna. Calculations have shown that, while the current or voltage peak value induced on the line, is practically proportional to the distance to the striking point and to the lightning current amplitude, the order of magnitude remains the same when the lightning striking point with respect to the line changes with the azimuth .. The paper proposes a theoretical model for the peak value computation of the current induced by an electromagnetic plane wave, with the Poynting vector parallel to the line, that illuminates an overhead transmission line. This represents a good guess for the amplitude of currents and voltages induced by strikes at any other positions. Different configurations are analyzed. The results given by the proposed model are compared to experimental results and to other theoretical models. This simple approach can be used for rapid estimation of lightning indirect effects on overhead lines in a maximizing analysis.